Based on the 21 work days in August '69, and the number of cars produced during Aug, the avg daily rate was 435/day.. assuming a single 8 hr shift that month, 196/435 ~ 3.6 hrs difference on the line...

Correct me if I am wrong but isn't the "pebble-grained" steering wheel that you are refering to and what GM refers to as the "grip assist" steering wheel the same? This should be included in the z23 option unless the wood grain wheel was ordered. Are you trying to document the factory's build accuracy as related to this option package?